1. Field of the Invention
The present invention relates to information recording systems and apparatus, and more particularly to a recording system and apparatus which records an information signal, a start and an end signal representative of the start and end of the information signal, respectively, and a data signal related to the information signal on a recording medium.
2. Related Background Art
In recently proposed video floppy systems it is proposed to record a video signal as well as an audio signal on a magnetic sheet provided as a recording medium.
FIG. 1 diagramatically shows both the video and audio signals present together on a magnetic sheet. For example, according to the standards on video floppies, field video signals (V) and audio signals (Al, A2) for up to 50 tracks in all can be recorded on a magnetic sheet. The audio signal is converted by time base compression into the video band and recorded in FM modulated form. The recording time per track is approximately 10 seconds, assuming that the audio band is 5 KHz and the time base compression ratio is 640. Also, assuming that the audio band is 2.5 KHz and the time base compression ratio is 1,280, recording for approximately 10 seconds is possible. In this case, the audio signal may be completed in a single track or extended into the next track.
The ring-like audio track is divided into four sectors, as shown in FIG. 2. For example, in the case where recording for 10 seconds is possible, an amount of information for 2.5 seconds is alloted to a single sector.
FIG. 3 illustrates the form of an audio signal and an additional signal to be recorded on a single sector.
In FIG. 3, after an elapse of t.sub.1 from time T.sub.0, a start ID signal having a level L.sub.H continues for time t.sub.2 for obtaining the timing to read audio signal information. After a blank of t.sub.3, the audio signal starts. During the preceding interval of time t.sub.4, the signal on a sector overlaps with that on the immediately preceding sector. This does not occur in the first sector corresponding to the leading portion of the audio signal. A new audio signal is in the remaining time t.sub.5, the length of which is variable; 2.5 seconds at a maximum in the mode of 10 seconds per track. After a subsequent blank of t.sub.6, an end ID signal having a level of L.sub.2 continues for t.sub.7 in order to detect the end of the audio signal and to obtain the timing of reading data signal related to the subsequent audio signal. After a blank of t.sub.8, the data interval continues for t.sub.9. Then a blanking interval of time t.sub.10 appears, the length of which is varied according to the interval t.sub.5 of the preceding audio signal, and thus one sector cycle ends. This form is basically the same in any of the sectors where the audio signal is present. The interval of the audio signal shown by t.sub.5 is variable and selected so that the interval t.sub.5 +t.sub.10 is constant at all times. Thus, the length of the audio signal determines the position of the end ID and data signals.
The data signal includes, in the form of digital data, the number indicative of the position, on the magnetic sheet, of a track on which the audio signal is recorded, the number of the leading and subsequent tracks through which audio signals are recorded continuously, the number of the tracks through which the video signal corresponding to the audio signal are recorded, the compression ratio of the audio signal, etc.
FIG. 4 shows an example of a device to reproduce an audio signal recorded in the form of a signal such as is mentioned above.
Reference numeral 1 denotes a magnetic sheet on which an audio signal, additional signals (ID and data signals) and a video signal such as are mentioned above are recorded. The magnetic sheet 1 is rotated at a constant speed by a motor 2 under control of a control circuit including a microcomputers, etc., (hereinafter referred to as the "MICOM"). In this case, the rotation speed is 3,600 rpm according to NTSC system on the assumption that one complete rotation of sheet 1 causes a one-field video signal to be recorded.
A PG head 3 detects a PG mark (not shown) provided on sheet 1. A PG detection circuit 4 outputs a PG signal of one pulse per unit rotation of sheet 1 on the basis of the output of head 3. The output of the PG detection circuit 4 is applied to MICOM 5.
A magnetic reproduction head 6 picks up audio and additional signals and delivers them through an reproduction amplifier 7 to an FM demodulator 8 by which is produced a demodulated signal which is then deemphasized by a deemphasis circuit 9 and supplied to an A/D converter 10.
When MICOM 5 is given a reproduction command, it causes A/D converter 10 to perform sampling at a predetermined frequency f.sub.VC and A/D conversion in accordance with the PG signal from PG detection circuit 4 and stores the output of the converter 10 in a memory 11.
As will be described later, the start point of the first sector of FIG. 2 is controlled at the time of recording so that it always has a constant phase relationship to the PG mark on sheet 1. Thus, the sampling and A/D conversion by A/D converter 10 and storage to memory 11 are performed according to the PG signal from the start point of the first sector.
In this way, when signals for one track are stored in memory 11, MICOM 5 starts to reproduce the audio signal while controlling an expansion ratio for audio reproduction, reproduction sequence, etc., on the basis of the data signal. That is, MICOM 5 reads the audio signals in memory 11 in address units and provides them to a D/A converter 12 at a frequency f.sub.AC corresponding to the expansion ratio. The output of D/A converter is produced as audible audio signals through a noise reduction circuit 13 from an output 14.
At this time, the position of head 6 on sheet 1 is controlled by a head drive circuit 15 under control of MICOM 5.
FIG. 5 is a flowchart for causing MICOM 5 to detect the start address for the audio signal in order to detect the data signal subsequent to the end ID signal, decode the contents of the data thereby to remove the additional signals, and extract the audio signal only.
The additional and audio signals reproduced by head 6 are stored in memory 11 (step 1). Initial conditions are set in counters, etc., required for detection of the additional and audio signals (step 2). The signals stored in memory 11 are read (step 3). It is determined whether the read signal is the start ID signal represented by high (or low) level (step 4). If the read signal is not the start ID, control returns to step 3 and the next stored signal is read, which will be repeated until the start ID signal is detected. When the start ID signal is detected, a level counter in another area of memory 11 counts a high (or low) level of the ID signal (step 5). It is determined whether or not high (or low) level has been counted n times successively (step 6). The steps 3-6 are repeated until such state has been reached. This eliminates noise and ensures that the start ID signal will be detected. After the start ID signal has been detected, the level of the start ID signal is assigned to the bits in memory 11 corresponding to the number of the sector to which the start ID is applied (step 7).
X addresses are skipped in the addresses of memory 11 within the level of the start ID signal to the address of a point before the trailing edge of the start ID signal (step 8). Then, the trailing edge of the ID signal is detected, that is, the stored signals are again sequentially read out of memory 11 (step 9). It is determined whether or not the read data is a position signal having a level equal to 90% of the high (or low) level of the ID signal and not a dropout (step 10). The steps 9 and 10 are repeated until the above conditions are satisfied. When the data signal is determined to be a position signal having a level equal to 90% of the high (or low) level of the start ID signal and not to be a dropout, the position signal is regarded as the trailing edge of the start ID signal, the start address of the audio signal is calculated from the address of the position signal, and this calculated address is stored in an address register set in another are of memory 11 (step 11).
In FIG. 3, while the start ID signal is shown sharply rising or falling, it will slowly rise or fall in fact. Therefore, only after the start ID signal has a value indicative of 90% of its high (or low) level, and no dropout (a sharp level drop for only one to a few bits) is detected, the trailing edge of the start ID signal is detected. The start address of the location where the audio signal is stored is calculated by adding the address bits corresponding to the interval t.sub.3 to the address of the trailing edge. Then the stored signals are read sequentially out of memory 11 at the start address of the audio signal calculated at step 11 (step 12). It is determined whether or not the end ID level is of high (or low) level (step 13). The steps 12 and 13 are repeated until the end ID is detected. After the end ID has been detected and in order to ascertain the end ID, the above level counter counts high (or low) levels (step 14). It is determined whether or not n successive high (or low) levels have been counted (step 15). The steps 12-16 are repeated until n successive high (or low) levels are counted. When n high (or low) levels have appeard, shipping is performed by z addresses to the address of a point immediately after the trailing edge of the end ID (step 16). After this skip, a synchronizing signal (hereinafter referred to as the "sync" contained in the data signals is detected out of the signals stored in memory 11 (step 17). It is determined whether or not the sync has been detected (step 18). The steps 17 and 18 are repeated until the sync has been detected. After the sync has been detected, the data signal is read (step 19). The contents of the data signal are decoded by MICOM 5 (step 20). The result is stored in a data signal register provided in another area of memory 11 (step 21). Then, sectors are counted by a sector counter provided in another area of memory 11 (step 22). It is determined whether or not the above flow operation has been performed on each of the four sectors by determining whether the contents of the sector counter is 4 (step 23). When the flow operation has not been completed for all the four sectors, address shipping or jumping is performed by y addresses to the address of a point immediately before the leading edge of the start ID of the next sector (step 24). The steps 3-23 are repeated for all the four sectors. Correct data information is determined by the information in all the four sectors and stored in a register provided in another area of memory 11.
In the above manner, the audio start address of each sector and correct information are obtained. However, if the data signal follows the end ID, as mentioned above, the detection of the data signal must be performed after detection of the start and end IDs. That is, detection of the end ID is indispensable. In addition, since the length of the audio signal between the start ID and the end ID is variable, a jump in address from the start ID to the end ID is impossible, the signals stored in memory 11 must be retrieved through the length of the audio signal until the end ID is detected. According to the foregoing, the steps 12-16 correspond to the processing from the detection of the start ID to the detection of the end ID. If the audio signal has been recorded at its maximum length in a sector, it will take a few seconds for MICOM 5 to detect the end ID, which is a large time loss compared to the case where the steps 12 to 16 are omitted. On the other hand, when the video and audio signals are reproduced concurrently, the information obtained by the foregoing is used for control of the reproduction. Therefore, the audio reproduction starts after a time loss of a few minutes and hence great non-coincidence in time between the reproduced video and audio signals results. In video-audio concurrent reproduction, when the data signal is being reproduced, no information on the data signal is available until after the end ID and hence the information on the compression ratio of the audio signal as mentioned above is not available. This renders concurrent reproduction of video and audio signals substantially impossible.
As described above, since the data signal is after the end ID, the access to data is slow, which, as a result, will be an obstacle to the reproduction processing.
In addition, if, for example, two memories, each memory having a memory capacity for one sector, should each be provided for a respective one of an even and an odd sectors and the stored signals should be read out of the corresponding memory while being recorded in the corresponding sectors, the tail end portion of each sector, i.e. the data signal portion, may be damagingly superimposed on the signal in the next sector. In this case, the reproduction processing of these data signals would be substantially impossible.